Controlling ready mixed concrete sludge water

ABSTRACT

Method and system for concrete wash-out water re-use, wherein an apparatus such as a mixing truck ( 1 ) is washed out and sludge ( 2 ) water re-used. The invention comprises providing sensors ( 11 ), in a communication system connected with a control center ( 10 ), for determining amount of retarder ( 4 ) used and resulting sludge water/concentration. The data is analyzed such that overdoses or insufficient doses of retarder are minimized or prevented. Warnings or corrective signals can then be sent by the control center ( 10 ) if needed.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method for controlling aconcrete sludge water, such as the water used for producing aready-mixed concrete or a precast concrete, by washing a mixing drum orother container apparatus in which the concrete was mixed or in which itis adhered, the washing involving a retarder-containing sludge water;removing aggregates from the wash sludge water; and reusing the sludgewater thus obtained as part of a mixing water for a fresh batch ofconcrete, on the next day or after the next day, without dischargingwaste from the concrete plant. The invention permits detection ofexcessive or insufficient retarder amounts added to the sludge water,and allows operators to cope instantly with these circumstances.

[0002] As taught in the prior art, Japanese Patent Publication (Kokai)No. Hei 2-263100/1990 (Pat. No. 265137), it is known to wash a mixingapparatus (in which the concrete adheres) with a retarder-containingwater, separating aggregates from the wash water, storing the sludgewater thus obtained in a manner so as to retain the activity of theconcrete therein, and reusing the sludge water in mixing water for afresh batch of concrete on or after the next day of operations. No lessthan 200 concrete plants currently employ this method and consequentlyceased discharging deactivated concrete wastes. As the generation ofconcrete-polluted water has ceased, there has been environmentaladvantages and the conservation of resources.

[0003] Still, concrete plants involve many open-air operations, and thewater content, aggregates, and other constituents of concrete can varyfrom day-to-day. Sand and gravel are natural materials used in concrete,and their compositions may vary. Although concrete is an industrialproduct, there are variations in the components due to variations in thepractices and materials of each manufacturer, the equipment of theconcrete plant, and other factors. Accordingly, the accurate control ofconcrete is difficult. Various types of concrete admixtures have beendeveloped, and concrete is produced according to the specification of aconstruction company and transported by an agitator vehicle to theconstruction site by skilled technologists who are needed for sufficientproduct control.

[0004] In addition, the amount of a retarder to be added is not fixedand may vary greatly due to the changes in the seasons. For example, ifthe day after a mixing and pouring is a holiday, a retarder will beadded in a large quantity. Also, the concentration of solids can alsogreatly affect the amount of retarder in the sludge water. Thus,maintaining control over the amount of retarder added into the concreteat the plant has been rather difficult.

[0005] Adding to these difficulties is the fact that dispensers, whichsupply retarder materials from tanks, are located in open air andsometimes broken down by the effects of wind and rain, and particularlyby thunderstorms. Another factor to consider is that many plants areunattended at night. Of course, there is also the possibility of simplemistakes due to operator error, which necessitates double and triplechecking. Thus, it is not surprising sometimes to find that retardersare sometimes dosed in amounts two to six times greater than actuallyrequired. Concretes prepared with sludge waters containing such largeamounts of retarder do not advance operations at the construction sitedue to the variable and often extended retarding of setting, and this isthe trouble that frequently arise where concrete plants are concerned.

[0006] Another problem is that if the retarder amount is deficient, theconcrete will have lost some of its activity, and when mixed with freshconcrete it will be difficult to mix, and this can result in a concretemix that is naturally deteriorated. In order to retain quality, theprovider of the concrete sometimes disposes of the concrete, an actionwhich is contrary to the purpose of using retarder technology in thefirst place.

[0007] Control over the accuracy in the dosing of retarders is anessential matter for concrete plant operations, but this is far fromperfect because the number of highly qualified technologists stationedat concrete plants is sometimes not adequate.

SUMMARY OF THE INVENTION

[0008] An objective of the present invention is to avoid the problems ofprior art practice in controlling retarder levels by providing sensorsin a communication system to transmit a signal, corresponding to theamount of retarder in a retarder tank, after completing an operationwherein a retarder is mixed into a concrete (e.g., concrete forready-mix or precast, for example), to a control center; and the signalwhich has detected the amount and the concentration of the sludge waterin a sludge tank to the control center are provided to avoid problemscaused by introducing excess retarder during washing operationsinvolving mixing drums, containers, or other devices in which concretehas been mixed with a retarder-containing water, separating aggregatesfrom the washed water and reusing the sludge water thus obtained as thepart of a mixing water of fresh concrete on and the after the next.

[0009] Thus, an objective is to provide a method of controlling aconcrete sludge water, a method involving detecting whether an excess ordeficiency of retarder is added to sludge water. This allows theoperator to make an adjustment, thereby avoiding the need to have todischarge waste concrete and/or sludge water from the plant. Theoperator may wash the mixer or apparatus in which the concrete isadhered with a retarder-containing water, remove aggregates from thewash water, and reuse the sludge water as the part of a mixing water forfresh concrete on or after the next day of operation.

[0010] An exemplary method of the invention thus comprises washing anapparatus to which concrete has been adhered with a retarder-containingwater, removing aggregates from the washed water and reusing the sludgewater as the part of a mixing water of fresh concrete on or after thenext day of operation, the invention being characterized by providing,in a communication system connected to a control center, a first sensoroperative to transmit a signal to control center corresponding to theamount of retarder in a retarder tank after completion of operations(e.g., after washing out the mixing truck) and a second in thecommunication system connected to a control center, the second sensoroperative to transmit a signal to the control center corresponding tothe amount and/or concentration of sludge water in a sludge tank. Thecontrol center thereby permits dosage of retarder into the sludge tankto be adjusted more accurately, so as to avoid problems that can becaused by introducing excessive amounts of retarder.

[0011] Further advantages and benefits of the invention will be furthercomprehended in view of the following detailed descriptions that follow.

BRIEF DESCRIPTION OF THE DRAWING

[0012]FIG. 1 is a schematic diagram of an exemplary method and system ofthe present invention, wherein an exemplary waste sludge water re-usesystem is connected to a control system, which in turn can be connectedto one or more waste sludge water re-use systems.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0013] In a concrete plant, after the last mixing truck or otherconcrete conveying vehicle has been washed out, it is now possible, byapplication of the method and system of the present invention, to avoidgenerating sludge water wastes at night.

[0014]FIG. 1 illustrates that two or more exemplary waste sludge waterre-use systems (each system comprising the components designatedgenerally as at 1-6, 8, 9, and 11) can be connected to a control system10, that can be located on the same premises or at a different premises.Alternatively, the two sets of waste sludge water re-use systems can belocated on the same or different premises from each other, and/or on thesame or different premises from the control system 10. For example, thecontrol system 10 can be connected to any number of different users(i.e., different waste sludge water re-use systems) by telephone orinternet.

[0015] After the sludge water is used for washing out the last truck fora given day's operation, the entire sludge water 2 is stored in a sludgetank 5, as shown in FIG. 1, and slowly stirred in the presence of anecessary and sufficient amount of a retarder. On the basis of theconcentration of concrete in the sludge water added with an exact amountof the retarder, the amount of the sludge water to be used in mixingfresh concrete on the next day together with the amounts of concrete andfresh water to be reduced in accordance therewith is calculated.

[0016] Accordingly, as shown for purposes of illustration at the uppercorner of retarder tank 4, there is provided by the present invention asensor 11, such as an ultrasonic level sensor, to transmit to a controlcenter or system 10 a signal corresponding to the level of the retarderin tank 4. The tank level is detected after completion of operations. Inthe control center 10, an abnormally small or large amounts of addedretarder may be sensed by statistical comparison from data accumulatedby the control center 10, and this can result for example in a report tothe concrete plant so that the abnormal retarder level can brought tothe attention of personnel at the concrete plant, or, as anotherexample, the dispenser 6 from the retarder tank 4 can be opened orclosed depending on the circumstances.

[0017] Furthermore, when an ultrasonic level sensor, shown forillustrative purposes designated as 8 at the upper right corner of theis sludge water tank 5, is provided, and an ultrasonic concentrationsensor 9 or the like is provided, as shown for illustrative purposes atthe lower right corner of the sludge water tank 5, the amount andconcentration of the sludge water can detected by these sensors. Thisinformation obtained thereby can also be transmitted to control center10. From the amount and concentration of the sludge water in sludgewater tank 5, the amount of concrete to be kept active can becalculated. The data collected may be used for determining whetherrelatively large or small amounts of retarder exist in the sludge water,and trouble can be avoided by having the control center report theabnormally large or small retarder amounts to the particular concreteplant, by having the control center open or close the dispenser toadjust the retarder dispenser accordingly, such as on a day to daybasis. The data can also be used to adjust retarder additions whensludge water is subsequently used for making fresh concrete.

[0018] As a way to ensure accuracy in the amount of the retarder beingdosed, it is preferable to employ a reducing sugar, such as glucose, andtest paper that indicates by color changes, when the paper is dipped inthe sludge water, the presence and relative amount of the reducing sugarpresent in the sludge water. Hence, an exemplary method of the inventioncomprises detecting the amount of the retarder in the sludge water byadding a reducing sugar to the retarder to visually determine theactivity of the concrete in the sludge water by the color reaction withsaid reducing sugar. Further exemplary methods comprise detecting theamount of the retarder in the sludge water by moistening with the sludgewater a test paper obtained by allowing a filter paper to adsorb areagent to exhibit a visually recognizable color reaction with thereducing sugar and drying the moistened filter paper. The reducing sugaris preferably glucose, dextrose, or mixture thereof; and the reagentpreferably comprises glucose oxides, peroxides, o-toluidine, or mixturesthereof.

[0019] An exemplary working mode of the invention is described asfollows. The term “apparatus” as used herein and after refers to amixing truck, tank, or other vessel to which concrete (e.g., ready-mix,precast) has been adhered and which requires a washing operation. Thus,the term apparatus may refer to the drum of an agitator vehicle (e.g.,ready mix truck) or to mixing containers as are used at the concreteplant sites where fresh concrete is produced.

[0020] Further, the term “retarder” as used herein means and refers toall compounds having the effect of generally retarding the setting ofconcrete, including hydroxycarboxylic acid compounds such as gluconicacid, citric acid and tartaric acid; sugars such as glucose, sucrose andlactose; aminophosphoric acid compounds and their salts, e g.,aminotrimethylene phosphonic acid; water reducing agents ofligninsulfonic acids and salts thereof which have no acceleratingaction; and silicofluorides. The term “sludge water” means and refers toa suspension of concrete or cement which still has activity (e.g.,having some ability to harden or to harden further).

[0021] A working exemplary embodiment of method and system of thepresent invention can be explained with reference to FIG. 1 as follows.

[0022] An agitator vehicle 1 (e.g., a ready mix truck), which is but oneexample of an apparatus to which concrete is adhered, is washed withsludge water from a sludge tank 2 which holds the wash water on atemporary basis. Subsequently, from this wash water, aggregates such assand and/or gravel are removed/recovered using in an aggregate separator3, and the resulting sludge water is again recovered in temporary sludgetank 2. Thus, the sludge water may be repeatedly used. Herein, when asufficient amount of a retarder from retarder tank 4 is added to thesludge water, which is also the wash water, the sludge water can berepeatedly used in washing operations while continuing to maintain theactivity of the concrete gradually to increase the concreteconcentration in the sludge water. When the sludge water reaches such ahigh concentration that causes an inconvenience in washing, the sludgewater is transferred from the temporary tank 2 to sludge tank 5, furtherdiluted with fresh water, and a retarder is added to permit furtherprocessing.

[0023] Thus, when the sludge water reaches or exceeds a predeterminedconcentration, it is stored in sludge tank 5 at a concentration of 20%or less (by weight). Because the sludge water is stored in the sludgetank 5 in a concentrated state for anywhere from one day to less than aweek later, a slow stirring means is used to prevent settling of theconcrete. Retarder is added into the sludge tank 5 from retarder tank 4through a dispenser 6 in an appropriate amount. The control over theappropriate amount dispensed is described below.

[0024] When used in the production of fresh concrete, the sludge fromsludge tank 5 should preferably not be added whereby the concretecontributing to the concrete feedstock exceeds 3% (wt.). A concreteplant which produces fresh concrete is designated at 7 in FIG. 1.Surplus sludge water that cannot be added to the concrete feedstock canbe mixed with fresh concrete on the next day or a day thereafter.Subsequently, it will follow that on some days, the entire amount ofsludge water can be used, and, on other days, only a portion of thesludge water can be used.

[0025] After the last agitator vehicle is washed out with wash water,the wash water is treated and transferred from temporary wash tank 2 andtransferred to sludge tank 5. In sludge tank 5, the appropriate amountof retarder to be added to the concentrated sludge water, for purposesof storage, can be determined by those of ordinary skill and will dependon seasonal influences, temperature, storage time, condensation, andother factors.

[0026] According to the present invention, a sensor 8 for detecting thevolume of the sludge water and a concentration sensor 9 for detectingconcentration of the sludge water are provided in the sludge tank 5.Signals from these sensors are transmitted to a control center 10 toenable calculation of the appropriate amount of the retarder to beprimarily added.

[0027] Furthermore, a sensor 11 for detecting the amount (e.g., volume)of the retarder is provided in the retarder tank 4, and a signaltherefrom is transmitted to control center 10, such that the volume ofretarder used and the volume of the retarder after completion of dailywash-out operations can be determined. In other words, the volume of theretarder used in one day together with the signal of the day before (andsignals from prior days as well) can be detected.

[0028] At control center 10, the data is collected and can be treated ona statistical basis, because the total amount and the concentration ofthe sludge water discharged from each day's operations and the dailyamount of the retarder used can be calculated. This capability enablesreview as to whether the amount of retarder added has been too great ortoo little. Furthermore, at control center 10 all the signals from thesensors can be detected.

[0029] When the amount of the retarder added is determined, after reviewof the data, to have been too much or too little, the control center canreport this result to the particular plant and/or transmit a signal tocarry out a further operation, such as to open or close the valve fromthe dispenser.

[0030] Sensor devices suitable for use in the present invention, such assensors for detecting volume of fluids, are available. For example,there exist sensors that utilize reflection principles based onultrasonic waves and the like. For detecting concentration levels,sensors are known based on ultrasonic operation, specific gravitymethods, electrical detection based on variation of impedance, and thelike. In addition, optical sensors are available for detectingconcentration based on detection of light scattered by colloidalsystems. In addition, the aforementioned communication system which maybe used for rendering the sensors in communication with the controlcenter 10 may be any system that can accomplish the above describedobjectives, including, for example, the NTT-DOPA network, a telephonenetwork, the I-mode (portable telephone) internet, the intranet, andother known means.

[0031] Furthermore, the means for transmitting signals from each plantis not limited. Preferably, the transmission means permits transmissionto be confirmed, and for the ability of the control center 10 to sendwarnings to each plant, if necessary or required, depending on the modeof the returned signals.

[0032] In addition, for safety's sake, it is preferred to add a reducingsugar having retarding properties, such as glucose, to the retarder toenable the amount of retarder to be determined. Thus, further exemplarymethods of the invention comprising detecting the amount of retarder inthe sludge water by adding a reducing sugar to the retarder to visuallyrecognize the activity of the concrete in the sludge water by the colorreaction with said reducing sugar.

[0033] The detecting reagent biochemically detects hydrogen peroxide tobe formed by using an enzyme such as glucose oxidase and galactoseoxidase in the enzymatic method or detects by a chemical method. Aboveall, glucose forms hydrogen peroxide by the action of glucose oxidase,and then oxidizes o-toluidine by the action of peroxidase to give a bluecolor from a yellow color depending on the concentration of glucose.This reaction is sensitive, detectable in a short period of time, and isspecific to glucose.

[0034] In addition, there is the Bertrand method of adding a Fehling'ssolution to a sample liquid, and titrating Cu₂O which precipitatesdepending on the amount of the reducing sugar with H₂SO₄ or a standardsolution of acidic potassium permanganate, the Somogyi method oftitrating I₂ which Cu₂O having been produced by reducing CuSO₄ with areducing sugar in alkalinity liberates with KIO₃+KI with Na₂SO₃ orallowing the I₂ to give a color with a starch solution and the like.

[0035] The visual recognition in the present invention means a method bywhich one can judge with the naked eye without using a specificinstrument. Thus, the color reaction by which the presence of a reducingsugar can surely be judged is preferred.

[0036] However, all reactions that are accompanied by a change which thenaked eye can recognize, such as formation of turbidity, increase intransparency and change in the surface state are included.

[0037] A method which can judge the presence of a reducing sugar by acolor reaction or another change by allowing a filter paper topreviously adsorb a reagent, drying the resulting paper obtained paper,and dipping the paper thus prepared in the sludge water is preferred.Further, a method which comprises placing a sample water to be examinedin a glass tube and adding a reagent to the water dropwise to judge somechange is preferred.

[0038] Exemplary concrete sludge water re-use systems of the inventiontherefore comprise: a retarder dispenser 4 having a sensor 11 operativeto generate a signal corresponding to the level of retarder in aretarder tank 4; and a sludge tank 5 having a sensor 8 operative togenerate a signal corresponding to the level of sludge water in thesludge tank 5, the sludge tank further having a sensor 9 operative togenerate a signal corresponding to the concentration of sludge in thesludge water contained in the sludge tank 9. The signals can be fed intoa control center, or, as previously mentioned, into a communicationsystem the renders the sensors communicative with a control centerelsewhere on the premises or located on an entirely different premises.It is also within contemplation of the present invention that exemplaryconcrete sludge water re-use systems can involve numerous sets of tanksand sensors, located on different premises, operative to communicatewith the same master center 10.

[0039] The following examples are provided for illustrative purposes andnot intended to limit the scope of the invention.

EXAMPLE 1

[0040] A solution containing 20% of sodium gluconate and 15% of glucosewas used as the retarder.

[0041] In a plant A, the amounts of the retarder used every day sincethe first day of an month were 21, 18, 23, 0, 17, 19 and 93

, respectively. The day on which no retarder was added (0

) was a holiday. Since 93

was an abnormal amount, this fact was reported to plant A, and the nextmorning the retarder in sludge tank 5 was examined by dipping a testpaper in the sludge water. The test paper was the one obtained byimpregnating a filter paper with a mixed solution of 450 units ofglucose oxidase, 14 units of peroxidase and 8.4 mg of o-toluidine anddrying the resulting filter paper. The test paper turned fresh blue, anda danger of sending concrete with the use of this sludge water for freshconcrete as usual which would not set could be avoided.

EXAMPLE 2

[0042] The amount of the sludge water in sludge tank 5 in a plant A wasdetected by first sensor 8 and the sludge concentration was detected byconcentration sensor 9. Furthermore, the amount of the retarder wasdetected by second sensor 11. The retarder used was the same as inExample 1. The amount of the retarder used, the concentration of thesludge water and the amount of the sludge water which were detected in12 days were shown in Table 1. TABLE 1 Day Mon Tue Wed Thu Fri Sat SuMon Tues Wed Thu Fri Retarder 17 20 41 18 15 20 0 16 21 22 25 14 Used(l) Amount 13 11 20 11 12 13 0 15 17 12 14 17 Sludge Water (m³)Concentration 15 17 20 15 12 14 10 12 16 17 20 Sludge Water (%)

[0043] In plant A, the amount of the retarder used per day is about 15to 22

. On Wednesday, the third day, the amount of the retarder used was a bittoo much, but the concentration and the amount of the sludge water wereboth extremely high on this day. This predicts a large amount ofreturned fresh concrete (e.g., ready mix) and the remaining ready mixedconcrete, and accordingly requires a large amount of the retarder, andthus the control center did not send out any warning.

[0044] However, on Friday, the last day in Table 1, in spite of the highconcentration of the sludge water, the amount of the retarder used israther small. When the sludge is left to stand as it is, concrete whichwill lose its activity would be incorporated into fresh concrete in thenext morning. The quality of the products will naturally be reduced.Accordingly, the control center sent out a signal to open dispenser 6and to close dispenser 6 at the point of time when about 15

of the retarder were introduced and transmitted this instruction toplant A.

[0045] On the next morning, the test using the same test paper as inExample 1 was carried out and no color reaction was caused, and theactivity of concrete could finally be retained.

[0046] Thus, in operations involving washing with a retarder-containingwater, an apparatus such as a mixing drum, in or to which concrete hasbeen adhered; removing aggregates from the washed water; and reusing thesludge water as part of a mixing water for a fresh batch of concrete onthe next day after operations or after the next day of operations, thepresent invention provides numerous benefits: such as, avoidingdischarging wastes from the concrete plant; minimizing over-dosing orunder-dosing retarders into the sludge water; permitting the detectionof retarder dosage level after operations are completed and allowingoperators to cope instantly with dosage problems; avoiding the dangersof making fresh concrete with sludge water having excessive orinsufficient retarder levels; and making concrete with deactivatedconcrete. Thus, the present invention provides numerous benefits andavoids the dangers and disadvantages of prior art practices.

It is claimed:
 1. A method of controlling a concrete sludge water,comprising: washing an apparatus to which concrete has been adhered witha retarder-containing water; separating aggregate material from theresulting washed water; and reusing the sludge water thus obtained asthe part of a mixing water of fresh concrete on the next day or afterthe next day, the invention being characterized in providing a sensor ina communication system operative to transmit a signal corresponding tothe amount of retarder in a retarder tank.
 2. The method of claim 1wherein said sensor to detect the amount of the retarder in the retardertank is an ultrasonic level sensor.
 3. The method of claim 1 whereinsaid sensor is communicative with a control center.
 4. The method ofclaim 1 further comprising providing a sensor in said communicationsystem operative to transmit a signal corresponding with solids contentof sludge water in a sludge tank to said control center.
 5. The methodof claim 4 wherein said sensor operative to transmit a signalcorresponding with solids content of sludge water in a sludge tank tosaid control center is an ultrasonic level sensor.
 6. The method ofclaim 5 wherein said sensor operative to transmit a signal to a controlcenter corresponding to the level of retarder in a retarder tank andsaid sensor operative to transmit a signal to the control centercorresponding to the solids content in said sludge tank are ultrasoniclevel sensors.
 7. The method claim 1 further comprising activating adispenser connected to retarder tank in a concrete plant, which tank isdeficient in the amount of the retarder to be added, until attaining anappropriate concentration and closing the dispenser of the retarder inaccordance with the transmission to the control center through thesensor.
 8. The method of claim 1 comprising detecting the amount of theretarder in the sludge water by adding a reducing sugar to the retarderto visually recognize the activity of the concrete in the sludge waterby the color reaction with said reducing sugar.
 9. The method of claim 8comprising detecting the amount of is the retarder in the sludge waterby moistening with the sludge water a test paper obtained by allowing afilter paper to adsorb a reagent to exhibit a visually recognizablecolor reaction with a reducing sugar and drying the moistened filterpaper.
 10. The method claim 9 said reducing sugar is glucose, dextrose,or mixture thereof; and the reagent comprises glucose oxidase,peroxidase, o-toluidine, or mixture thereof.
 11. Concrete sludge waterre-use system, comprising: a retarder dispenser 4 having a sensor 11operative to generate a signal corresponding to the level of retarder ina retarder tank 4; and a sludge tank 5 having a sensor 8 operative togenerate a signal corresponding to the level of sludge water in thesludge tank 5, the sludge tank further having a sensor 9 operative togenerate a signal corresponding to the concentration of sludge in thesludge water contained in the sludge tank
 9. 12. The system of claim 11wherein said sensors are communicative with a communications systemoperative to receive signals from said sensors, said communicationssystem operative to render said sensors communicable with a mastercenter, whereby signals from said sensors may be received and collected.13. The system of claim 12 wherein said master center is operative tosend signals to a premises on which said sensors are located.